Opus Dei provides spiritual formation aimed at helping people develop their spiritual life and apostolate. These activities are held in Opus Dei centers or in a church, office or private home.

“Opus Dei's main activity consists in offering its members, and other people, the spiritual means they need to live as good Christians in the midst of the world," explained its founder.

Spiritual formation

The faithful of the Prelature attend weekly classes called “circles", dealing with doctrinal and ascetical topics, and a monthly day of recollection, a time for personal prayer and reflection on topics to do with Christian life. In addition, they attend an annual retreat lasting three to five days. Similar activities are also offered to the cooperators, to young people, and to anyone else who wishes to attend.

This formation is given in the centers of the Prelature and in other appropriate places. For example, a circle may be given at the home of one of the people who attend, and a day of recollection may be held in a church whose parish priest permits it to be used for that purpose.

Personal apostolate

Personal testimony is always the most important apostolate in Opus Dei. It is an apostolate of witness, of specific and effective help given to others, at work and in the other circumstances of daily life: a personal apostolate carried out through word and example. As a result, members' apostolic work is not limited to specific fields such as education, or care for the sick or disabled. As the Catechism of the Catholic Church reminds us, all Christians, whatever their secular occupation may be, ought to help to find Christian solutions to the problems of society and give constant witness to their faith.

Corporate apostolate

Some faithful of the Prelature, along with cooperators of Opus Dei and others, undertake charitable or educational initiatives which entrust their spiritual and doctrinal orientation to the Prelature. Among these apostolates are secondary schools, universities, women's centers, medical clinics in underdeveloped areas, schools for farm workers, institutes for professional education, student residences and cultural centers. These initiatives are always set up to meet a social need in the city or country where they are located. The Prelature does not involve itself in any for-profit, commercial, or political ventures.

These initiatives are called "corporate" apostolates to distinguish them from the personal apostolate of each member, which is Opus Dei's primary apostolate. A corporate apostolate is usually owned by a civil not-for-profit corporation and is managed by its own board of directors and administrative staff. The Prelature takes on responsibility for its spiritual and doctrinal orientation, guaranteeing that this orientation will be faithful to Catholic teachings. Despite this Christian orientation, these apostolates are open to persons of all religions and the legitimate freedom of conscience of all those involved is carefully respected.

Each undertaking is financed in the same way as other similar institutions: tuition, residential fees, grants, donations, etc. Given the type of work they undertake as non-profit institutions, corporate apostolates usually require substantial donations from the faithful of Opus Dei, cooperators and others. Frequently they also receive official subsidies from government agencies and grants from private foundations and companies.

In addition to the corporate apostolates, there are other institutions run by faithful of the Prelature and their friends in which the Prelature does not take on the responsibility for the spiritual and doctrinal orientation, but does give some help in this area, e.g., by supplying a chaplain for the institution.

Examples of corporate apostolates:

- The University of Navarra, founded in Pamplona, Spain, in 1952. It has 20 schools and institutes. The Pamplona campus includes a medical school with a hospital. A business school, the Institute for Higher Business Studies (IESE), is located in Barcelona. Other educational initiatives at the university level include the University of Piura (Peru), the University of La Sabana (Colombia), and the University of Asia and the Pacific (Philippines).

- Monkole, in Kinshasa, is a hospital which every year serves thousands of people in situations of extreme need. Medical assistance is also given at traveling dispensaries at two other locations outside the capital (Eliba and Kimbondo). Attached to Monkole is the Higher Institute of Nursing, which prepares young Congolese women for the nursing profession.

- Punlaan, in Manila, is a specialist professional school for the catering and tourist industry. Its educational system includes direct contact with hotels and restaurants, and in the last few years, 100% of the young women who have studied at Punlaan have been able to find suitable employment.

- Midtown Sports and Cultural Center in Chicago, situated in a multiracial neighborhood where many young people live, offers programs providing academic, human, spiritual, and athletic formation. The programs help compensate for some of the deficiencies in the local social environment., As reported in 2015, for the previous fifteen years 100% of Midtown's students had finished high school and gone on to attend college, a figure well above the average for young people in that area.

- Toshi, to the west of Mexico City, is an educational institute for women in a rural area populated by numerous ethnic groups. Among other activities, it offers administrative training to help women find positions in business and public life in nearby cities.